Today the main method for deep tissue imaging is endoscopy using fibers or grin lenses. The disadvantage of these methods is their poor resolution and very large size. They are also limited to very specific shapes. Also, because these GRIN lenses have a relatively low index contrast, their field of view (FOV) is usually much smaller than their actual size. For example, for a 2 mm GRIN lens, the FOV is only a few hundreds of microns. A device for deep tissue imaging with high resolution and better FOV is desired.
Optogenetics, a biological technique that uses light to excite and inhibit neurons, has revolutionized research in neuroscience (see Boyden, E. S., et al., “Millisecond-timescale, genetically targeted optical control of neural activity,” Nature neuroscience, 8.9 (2005): 1263-1268). At present, however, most applications of optogenetics employ a single optical fiber to flood a large area of the brain with light, which limits the ability to control and monitor single neurons. Optical microscopy techniques can alleviate this problem for areas of the brain close to the surface (see Packer, Adam M., et al., “Targeting neurons and photons for optogenetics,” Nature neuroscience 16.7 (2013): 805-815). However, single neuron targeting using such techniques deep in the brain remains a challenge due to the large scattering of light.
On-chip waveguides could enable monolithic integration of light with traditional electrical probes and the manipulation of light through filtering and routing in order to control single neurons in deep regions of brain, which are not accessible with microscopic techniques. Furthermore, on chip waveguides can be implanted chronically in behaving animals, which is impossible to do by optical microscopy. On-chip waveguides for optogenetic applications have recently been demonstrated by Zorzos, A N, et al. in “Multiwaveguide implantable probe for light delivery to sets of distributed brain targets,” Optics letters, 35.24 (2010): 4133-4135. However, most of on-chip platforms suffer fundamentally from low resolution and poor bandwidth. On-chip waveguides also rely on high index contrast materials such as for example SiN/SiO2 and are therefore limited to small cross sectional dimensions. This leads to high beam divergence of light exiting from the waveguides. In addition, several of the platforms demonstrated are highly dispersive and wavelength sensitive and therefore cannot be applied to applications requiring high bandwidth such as nonlinear excitation and simultaneous neural excitation using distinct wavelengths.
A device for deep tissue imaging with high resolution and better FOV, for optogenetic excitation, and for other related applications is desired.